Listric extensional fault systems - results of analogue model experiments

Abstract Analogue models are a powerful tool for investigating progressive deformation in extensional fault systems. This paper presents exciting new insights into the progressive evolution of hanging wall structures in listric extensional terranes. Analogue models, scaled to simulate deformation in a sedimentary sequence, were constructed for simple listric and ramp/flat listric extensional detachments. For each detachment geometry homogeneous sand, sand/mica and sand/clay models were used to simulate respectively, deformation of isotropic sediments, of anisotropic sediments and of sedimentary sequences with competency contrasts. Roll-over anticlines with geometrically necessary crestal collapse graben structures are characteristic of the steepening-upwards segments of listric extensional fault systems in all of our models. With progressive deformation, crestal collapse grabens show hanging wall nucleation of new faults. Variations in graben size, amount of fault rotation and throw, are dependent on detachment curvature and amount of extension. Individual faults and associated fault blocks may significantly change shape during extension. Complex and apparently conjugate fault arrays are the result of superposition of successive crestal collapse grabens. Ramp/flat listric extensional fault systems are characterized by a roll-over anticline and a crestal collapse graben system associated with each steepening-upwards segment of the detachment and a ramp zone consisting of a hanging wall syncline and a complex deformation zone with local reverse faults. The roll-over anticlines and crestal collapse graben are similar in geometry to those formed in simple listric extensional systems. The models demonstrate that the geometry of the detachments exerts a fundamental control on the evolution of hanging wall structures. Analysis of particle displacement paths for these experiments provides new insights into the mechanical development of roll-over anticlines. Two general models for deformation above simple listric and ramp/flat listric extensional detachments have been erected.     

Spatio-temporal Organization of Mountain Taiga Geosystems of the Baikal Natural Territory

Results from investigating the geosystems of Cisbaikalia in its western and eastern parts (Primorskii Range and Barguzin Range, respectively) are presented. For studying three macroslopes of these mountain ranges (having an easterly aspect for the Primorskii Range and a westerly and south-easterly aspect for the Barguzin Range), the regional background and the main factors of the landscape differentiation of the study areas were analyzed. Structural features of topological geosystems are revealed, and large-scale maps of key areas are compiled (at a scale of 1:50 000). Maps of the landscape-typological structure were created on the basis of the structural-dynamic and facies analysis of landscapes. It is established that the main factors influencing the landscape diversity are the aspect and steepness of the slopes, the composition and structure of rocks, the absolute height, the amount of atmospheric precipitation, and anthropogenic impacts. It is determined that the influence of the lithomorphic factor is widespread throughout the study areas, the hydromorphic factor is also important, the cryomorphic factor occurs additionally in the goletz zone, and the xeromorphic factor is only observed on the Baikal Range and on the coastal plain in some areas of Priolkhonie. The dynamic aspect of the landscape structure and the relationships between geosystems are displayed in map legends.